In a continuing series of studies of the connections of the hippocampal formation, it has become apparent that the input of this structues is, to a large extent, mediated by the cingulate cortex. I propose to investigate the connections of this latter area in the rat by using tracing methods which employ the physiological processes of anterograde and retrograde axoplasmic transport. The anterograde tracing method of choice will be the 3H-amino acid autoradiographic method, while the retrograde tracing will be carried out using the horseradish peroxidase method and the new fluorescence dyes method for double labeling. These data will be compared with a detailed cytoarchitectonic analysis of the cingulate cortex. The use of the autoradiographic tracing method will make it possible to examine the connections of this area without involving the various fiber systems which lie within or very close to the mesial cortex. The other methods employed will be extremely useful in further enhancing our detailed knowledge of these connections. Thus, the results of these studies should be of direct relevance to our understanding of the circuitry of this area, and more importantly, they should elucidate the organization of the entire limbic system.